I would love to! But I cannot imagine what I can say that would be unique. If people wanted to determine if a video were able to run universally on HTML5 streaming software, wouldn't they just use FFprobe and check the necessary stream metadata for compatibility upon output? Surely, these sites are using FFprobe already to determine other metadata within the video container files they receive from users?

I have always run under the assumption that sites like YouTube want to further compress all video uploads so that they can implement proprietary functionality dealing with the video content and its other important business services (ad sales, user agent scraping, data collection, etc.)